Dewey Decimal
System Lookup.
Find a book’s number.
Make sense of where it belongs.
Public catalogue records No account needed
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The ten Dewey Decimal System classes
Start with the first digit. Follow it to a more specific subject.
How to read a Dewey Decimal number
The first digit gives you a broad class. More digits narrow the subject. A local library can add letters and collection marks to make the full call number.
Learn to read a Dewey number ↗Look up a book by ISBN or title?
Use the information you have, then check the edition before using its number. An ISBN search and a title search begin at different points in that process.
Have an ISBN? Start with the edition.
Choose ISBN and enter the ten or thirteen digits printed on the book or its publication details. Spaces and hyphens are fine. The lookup checks catalogue records associated with that identifier, which is more specific than a title shared by several editions.
An identifier match is a starting point, not a complete identity check. Compare the returned title, author, publisher and publication information with your copy. A catalogue can contain an incorrect association, and a valid ISBN does not guarantee that a numeric Dewey field will be available.
Have a title? Choose the matching book.
Choose Title when you do not know the ISBN. A familiar title can return translations, revised editions, adaptations or unrelated books with the same name. Compare the author and the other details instead of assuming the first candidate is the right one.
Some candidates describe a work across several editions. Choose a matching ISBN, when one is offered, to check that edition’s catalogue records. A number found on another version remains a useful lead; it should not silently become a confirmed number for the copy you are trying to identify.
For example, our Atomic Habits edition page pairs 155.24 with ISBN 9780735211292 and a Library of Congress record. Searching only the title is a way to find candidates; checking that ISBN and record is what connects this example to an edition.
If you know the writer, Author search helps you find candidates to inspect. If you have a subject rather than a particular book, Topic search brings back related catalogue books. Their numbers are examples of how those books were classified, rather than a single classification automatically assigned to your topic.
Why can the same book have different Dewey numbers?
A Dewey result belongs with its source record. Two different numbers are a reason to compare the records, not a reason to choose whichever looks most precise.
First compare the editions.
A revised text, translation, abridgement or adaptation may share a title without being the same publication. Check the ISBN and publication details before comparing numbers. Even when two records list the same ISBN, inspect their titles and authors: shared identifiers do not independently prove that every field is correct.
Then compare what the records describe.
A book can cross subject boundaries. Catalogue records may reflect different judgements about its main focus, a different edition of the classification, or different levels of detail. A longer decimal is more specific, but that alone does not make it the best classification for every collection.
Keep classification and shelf location separate.
A library can shorten a number, place a book in a special collection, or use a local fiction or biography arrangement. Its full call number can also include letters, a date or collection marks. Use your own library’s catalogue for the location where you will actually find or shelve the book.
Keep the original field in view.
Catalogue formatting can look different without giving a different numeric value. For example, our Thinking, Fast and Slow record contains 153.4/2, displayed as 153.42. The slash is preserved in the source details; removing it for numeric reading does not assign a new classification.
Compare each number with its linked record and your copy. A source being unavailable is different from a record having no numeric classification. If the records still disagree, keep that uncertainty visible and ask your library which classification and shelf mark it uses. Our sources and methods explain how catalogue results, edition associations and failures are kept separate.
Example Dewey numbers for real books
More edition examples
- Atomic Habits155.24
- Learning Python005.117
- Mere Christianity230
- Sapiens909
- A Brief History of Time523.1
- Joy of Cooking641.5973
- The Design of Everyday Things745.20019
- Drawing on the Right Side of the Brain741.2
- Guns, Germs, and Steel303.4
- The Language Instinct400
- Salt, Fat, Acid, Heat641.5
- The Way Things Work Now600
- The Anxious Generation305.230973
- Educated270.092
Dewey Decimal System lookup: common questions
Catalogues offer evidence.
Your library has the final shelf location.
How do I find a Dewey number by ISBN?
Choose ISBN, enter the ten or thirteen digits and search. Compare the title, author and edition in the returned records. Each numeric result links to its catalogue source. Your own library may use a different shelf mark.
Can I search by title, author or topic?
Yes. These searches return book or work candidates. Choose the matching book and an ISBN to check its edition. Topic results show numbers from related catalogue books; they are examples to compare, not a unique number automatically assigned to your topic.
Why does a novel show FIC instead of a number?
Many libraries organise fiction alphabetically and use a marker such as FIC. That marker is useful catalogue information, but it is not a numeric Dewey classification. A missing number does not mean the book is missing from every library.
Why do sources give different numbers?
Catalogues can differ in edition, scope, detail, classification edition or local practice. A shared ISBN is a useful association, not a guarantee that all metadata is correct. Compare the source records and check with your library.
What does “From catalog record” mean?
The number appears in the linked public bibliographic record. It does not mean this site assigned the number, that a librarian independently reviewed this result, or that the source institution endorses this site.
Is this the complete official Dewey database?
No. Dewey Number is an independent lookup and learning site. It retrieves available public catalogue records and explains them. The official classification schedules and WebDewey are maintained by OCLC.
Where our Dewey numbers come from
We look for classifications in public catalogue records and show the differences. Some books have no numeric Dewey record; a source can also be temporarily unavailable.